Positive electrode active material for non-aqueous electrolyte secondary batteries, and non-aqueous electrolyte secondary batteries

Abstract

The present invention relates to a positive electrode active material described in the claims and specification, a method of using the same to suppress thermal runaway in a non-aqueous electrolyte secondary battery, and a non-aqueous electrolyte secondary battery using the positive electrode active material.

Description

[Technical Field]

[0001] The present invention relates to a positive electrode active material for a non-aqueous electrolyte secondary battery, a method of using the same to control oxygen release from the positive electrode active material and / or to suppress or avoid thermal runaway in a non-aqueous electrolyte secondary battery, and a non-aqueous electrolyte secondary battery comprising the said material. [Background technology]

[0002] Lithium-ion rechargeable batteries have several advantages, including being small, lightweight, having high energy density, high charge / discharge voltage, and large charge / discharge capacity, making them a popular power source for electronic devices such as AV equipment and personal computers.

[0003] Typically, lithium-ion secondary batteries use mainly flammable organic solvents as their electrolyte, requiring high thermal stability. For example, when a lithium-ion secondary battery is charged, oxygen is released due to the heat within the positive electrode active material crystal. It is known that this oxygen reacts with the electrolyte, causing thermal runaway.

[0004] In recent years, active materials containing Ni, Co, and Mn have become widely used as positive electrode active materials. With this type of positive electrode active material, if the Ni content is high, a phase transition reaction occurs in the positive electrode active material at low temperatures, and oxygen is rapidly released, making the positive electrode active material prone to thermal runaway. On the other hand, with the increasing capacity of batteries, materials with high Ni content are required, and as a result, the thermal stability, which is a characteristic of materials with high Ni content, tends to decrease.

[0005] In order to suppress the thermal runaway of such a positive electrode active material, for example, Patent Document 1 proposes a positive electrode active material containing a lithium-transition metal composite oxide containing 80 mol% or more of Ni and 0.1 mol% to 1.5 mol% of B with respect to the total molar number of metal elements excluding lithium. Here, at least on the particle surface of the lithium transition metal composite oxide, B and at least one element M1 selected from Group 4 to Group 6 are present. When particles with a volume-based particle size larger than the 70% particle size (D70) are defined as first particles and particles with a volume-based particle size smaller than the 30% particle size (D30) are defined as second particles, the molar fraction (A2) of M1 with respect to the total molar number of metal elements excluding Li on the surface of the second particles is larger than the molar fraction of M1 with respect to the total molar number of metal elements excluding Li on the surface of the first particles. And Patent Document 1 shows that by using such a composite oxide in a lithium-ion secondary battery, self-heating is suppressed even at high temperatures.

Prior Art Documents

Patent Documents

[0006]

Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0007] However, in the positive electrode active material of Patent Document 1, since the particle surface of the positive electrode active material is covered with a boron compound, although a certain effect of suppressing the thermal runaway caused by the reaction between the oxygen released from the positive electrode active material and the electrolyte can be expected, a sufficient effect of suppressing the thermal runaway cannot be obtained only by this, and there is still room for improvement.

[0008] Therefore, a method for suppressing thermal runaway other than the above method of covering the surface of the positive electrode active material with a compound is required.

[0009] The present disclosure was devised in view of the above circumstances, and an object thereof is to provide a positive electrode active material capable of suppressing thermal runaway of a non-aqueous electrolyte secondary battery, and a non-aqueous electrolyte secondary battery using this positive electrode active material.

Means for Solving the Problems

[0010] The inventors of the present invention conducted intensive studies to solve the above problems. As a result, when the volume-based particle size frequency distribution of the primary particles of a composite oxide containing at least lithium and a transition metal is separated into a plurality of peaks, these peaks include a main peak showing the maximum value of the peak area, and at least one peak having an area of 0.1 to 1 in terms of the area ratio to the area of the main peak, and the inventors conceived of a positive electrode active material in which the ratio (large particle size / small particle size) of the primary particle diameters at the peak tops of adjacent specific peaks is both 1.2 to 8. When such a positive electrode active material is used in a non-aqueous electrolyte secondary battery, it has been found that the maximum oxygen release rate (hereinafter referred to as "maximum oxygen release rate") from the positive electrode active material can be limited, and thermal runaway can also be suppressed. Specifically, the present disclosure provides the following features.

[0011] (1) In a first aspect, the present invention relates to a method of using a positive electrode active material for a non-aqueous electrolyte secondary battery for suppressing or avoiding thermal runaway of the non-aqueous electrolyte secondary battery. The positive electrode active material includes a composite oxide containing at least lithium, a transition metal, and oxygen. When the volume-based particle size frequency distribution of the primary particles of the composite oxide is separated into a plurality of peaks, these peaks include a main peak showing the maximum value of the peak area, and at least one peak having an area of 0.1 to 1 in terms of the area ratio to the area of the main peak, and the ratio (large particle size / small particle size) of the primary particle diameters at the peak tops of adjacent specific peaks is both 1.2 to 8.

[0012] (2) In a second embodiment, the present invention relates to a method for using a positive electrode active material for a non-aqueous electrolyte secondary battery to control oxygen release from the positive electrode active material, wherein the positive electrode active material comprises a composite oxide containing at least lithium, a transition metal and oxygen, and when the volume-based particle size frequency distribution of the primary particles of the composite oxide is separated into a plurality of peaks, these peaks include a main peak showing the maximum peak area and at least one peak having an area ratio of 0.1 to 1 with respect to the area of ​​the main peak, and the ratio of the particle sizes of the primary particles at the peak tops of adjacent specific peaks (large particle size / small particle size) is 1.2 to 8 in all cases.

[0013] (3) In a third embodiment, the present invention relates to a positive electrode active material for a non-aqueous electrolyte secondary battery, wherein the positive electrode active material comprises a composite oxide containing at least lithium, a transition metal, and oxygen, and when the volume-based particle size frequency distribution of the primary particles of the composite oxide is separated into a plurality of peaks, these peaks include a main peak that shows the maximum peak area and at least one peak having an area ratio of 0.1 to 1 with respect to the area of ​​the main peak, and the ratio of the particle sizes of the primary particles at the peak tops of adjacent specific peaks (large particle size / small particle size) is 1.2 to 8 in all cases.

[0014] The composite oxide is preferably a lithium-nickel composite oxide. More preferably, it has a layered rock salt structure and the general formula Li a Ni 1-b-c Mn b M c O2 is a lithium-nickel composite oxide represented by the formula O2 (wherein M is at least one element other than Li, Ni, Mn, and O, and 0.95 ≤ a ≤ 1.15 and 0 ≤ b + c ≤ 0.70).

[0015] In the positive electrode active material for non-aqueous electrolyte secondary batteries disclosed in (1), (2), or (3) above, or in the following preferred embodiments, the particle size of the primary particles at the peak top of a particular peak is preferably 80 nm to 15 μm.

[0016] (4) In a fourth embodiment, the present invention relates to a non-aqueous electrolyte secondary battery comprising a positive electrode containing a positive electrode active material disclosed in (3) or in the above or below preferred embodiments thereof. [Effects of the Invention]

[0017] The present invention provides a positive electrode active material capable of suppressing thermal runaway by controlling the particle size of primary particles present in the positive electrode active material, and a non-aqueous electrolyte secondary battery using the positive electrode active material. [Brief explanation of the drawing]

[0018] [Figure 1] Figure 1A is an example of a scanning electron microscope image of a complex oxide. Figure 1B shows the same scanning electron microscope image of the complex oxide in Figure 1A, with the primary particles enclosed by dashed lines. [Figure 2] Figure 2 is a volume-based particle size frequency distribution diagram of primary particles in the positive electrode active material sample according to Example 1. [Figure 3] Figure 3 shows the DTG (differential thermogravimetric analysis) curve of the positive electrode active material sample according to Example 1. [Figure 4] Figure 4 is a volume-based particle size frequency distribution diagram of primary particles in the positive electrode active material sample according to Example 2. [Figure 5] Figure 5 shows the DTG curve of the positive electrode active material sample according to Example 2. [Figure 6] Figure 6 is a volume-based particle size frequency distribution diagram of primary particles in the positive electrode active material sample according to Example 3. [Figure 7] Figure 7 shows the DTG curve of the positive electrode active material sample according to Example 3. [Figure 8] Figure 8 shows the volume-based particle size frequency distribution of primary particles in the positive electrode active material sample according to Example 4. [Figure 9] Figure 9 shows the DTG curve of the positive electrode active material sample according to Example 4. [Figure 10] Figure 10 shows the volume-based particle size frequency distribution of primary particles in the positive electrode active material sample according to Comparative Example 1. [Figure 11] Figure 11 shows the DTG curve of the positive electrode active material sample according to Comparative Example 1. [Modes for carrying out the invention]

[0019] The embodiments of this disclosure will be described below, but this disclosure is not limited in any way by the description of the embodiments and can be implemented with appropriate modifications.

[0020] Unless otherwise specified, references to preferred embodiments apply to both the method of use of the present invention and the positive electrode active material of the present invention, as well as to the secondary battery of the present invention.

[0021] <Positive electrode active material for non-aqueous electrolyte secondary batteries and its use> A positive electrode active material for a non-aqueous electrolyte secondary battery according to one embodiment of the present disclosure comprises a composite oxide containing at least lithium, a transition metal, and oxygen, wherein when the volume-based particle size frequency distribution of the primary particles of the composite oxide is separated into a plurality of peaks, these peaks include a main peak showing the maximum peak area and at least one peak having an area ratio of 0.1 to 1 with respect to the area of ​​the main peak, and the ratio of the particle sizes (large particle size / small particle size) of the peak tops of adjacent specific peaks is 1.2 to 8 in all cases.

[0022] The inventors have found that the temperature at which a composite oxide releases oxygen correlates with the particle size distribution of the primary particles of the composite oxide. Specifically, the larger the particle size of the primary particles of the composite oxide, the higher the oxygen release temperature. The inventors performed DTG measurements on the composite oxide and confirmed by TG-MS (thermogravimetric mass spectrometry) that substantially all of the mass loss at temperatures below approximately 310°C is due to oxygen release. Furthermore, they found a correspondence between the temperature of each peak top obtained when the DTG curve is separated into oxygen release peaks and the particle size of each peak top obtained when the particle size frequency distribution is separated into peaks.

[0023] Furthermore, it was found that the amount of oxygen released from the composite oxide particles depends on the area of ​​each peak obtained when the particle size frequency distribution of the primary particles of the composite oxide is separated into peaks.

[0024] If the particle size of the primary particles of the composite oxide is such that there is only one sharp peak in the particle size frequency distribution and the particles are arranged in a way that prevents separation into a single peak (see Figure 10), or if the particles can be separated into multiple peaks but are close together, then in the DTG curve, oxygen is released from the primary particles within a specific narrow temperature range (see Figure 11). This oxygen reacts with the electrolyte, causing a rapid exothermic reaction and thermal runaway.

[0025] In contrast, in a positive electrode active material according to one embodiment of the present disclosure, the volume-based particle size frequency distribution of the primary particles of the composite oxide can be separated into multiple peaks (specific peaks) with a certain area or larger relative to the main peak (see Figure 2). Furthermore, in such a composite oxide, the oxygen release peak in the DTG curve can be separated into individual peaks (see Figure 3). Moreover, the presence of peaks with a certain area or larger in the particle size frequency distribution of the primary particles means that a certain amount or more of oxygen is being released. This further means that by providing multiple such specific peaks, the temperature at which a certain amount or more of oxygen is released can be divided into multiple temperatures.

[0026] Furthermore, by setting the ratio of primary particle sizes corresponding to the peak tops of adjacent specific peaks, multiple primary particles with a certain difference in size exist together at each peak top in the particle size frequency distribution. As a result, a large difference is created in the temperature at which a certain amount of oxygen is released, and by dispersing the oxygen release amount and temperature, it becomes possible to suppress the rapid heat generation of the electrolyte.

[0027] Although it was stated above that "...multiple primary particles are present together," it is not necessarily required to mix multiple primary particles. Furthermore, some composite oxides with multiple specific peaks are synthesized in their original state, and such composite oxides can also be used without mixing. Moreover, even if a composite oxide has multiple specific peaks, it can be mixed if the respective peaks maintain the relationships described above after mixing.

[0028] Below, Li 1-x-δ Using NiO2 (where x+δ indicates the amount of Li released from LiNiO2 upon charging) as an example, we will explain the mechanism by which a composite oxide releases a large amount of lithium from within its crystal structure when it is charged, and releases oxygen in a generally unstable crystal structure. When such a composite oxide is used as a positive electrode active material and heated in a charged state, the crystal state undergoes a phase transition from a layered rock salt structure (R-3m) to a spinel structure (Fd-3m) or rock salt structure (Fm3m) within a specific temperature range, as shown by equations (1) and (2) below. The temperature of these phase transitions depends on the depth of the charge, but the phase transition occurs in a temperature range of approximately 190 to 310°C. Furthermore, as is clear from equations (1) and (2), it is thought that the phase transition proceeds while generating oxygen.

[0029] Formula (1): Li 1-x-δ NiO2 (Layered rock salt structure R-3m) →{(1-x-δ) / (1-δ)}Li 1-δ NiO2 (Layered rock salt structure 1 R-3m) +{x / 3(1-δ)}Ni3O4 (Spinel structure Fd-3m) +{x / 3(1-δ)}O2↑ Formula (2): ●{(1-x-δ) / (1-δ)}Li 1-δ NiO2 (Layered rock salt structure 1 R-3m) →(1-x-δ)LiNiO2 (Layered rock salt structure 2 R-3m) +{δ(1-x-δ) / (1-δ)}NiO(Halite structure 1 Fm3m) +{δ(1-x-δ) / 2(1-δ)}O2↑ ●{x / 3(1-δ)}Ni3O4 (Spinel structure Fd-3m) →{x / 3(1-δ)}NiO (rock salt structure 2 Fm3m) +{x / 6(1-δ)}O2↑

[0030] Note that the 3 in R-3m usually has a hyphen, but for convenience, it is written as above. Similarly, the 3 in Fd-3m also has a hyphen, but for convenience, it is written as above.

[0031] The inventors hypothesized that the rapid generation of oxygen gas would have a significant impact on the thermal stability of a charged non-aqueous electrolyte secondary battery.

[0032] When a charged non-aqueous electrolyte secondary battery overheats and its temperature rises, oxygen gas is generated by the reaction in equation (1) or equation (2). As a result, the organic electrolyte in the non-aqueous electrolyte secondary battery is mainly oxidized (including combustion). Since this reaction is exothermic, the temperature of the non-aqueous electrolyte secondary battery rises. This temperature rise further causes oxidation of the electrolyte and generates heat, so if the temperature rise becomes uncontrollable, it leads to thermal runaway.

[0033] The temperature rise is proportional to the difference between the amount of heat generated per unit time in a non-aqueous electrolyte secondary battery and the amount of heat dissipated per unit time from the non-aqueous electrolyte secondary battery. Therefore, by preventing the amount of heat and heat flow generated by equations (1) and (2) from concentrating in a short period of time, the temperature rise can be suppressed, preventing uncontrollable thermal runaway and improving safety.

[0034] Based on the above, the inventors believe that the most important thing in order to suppress uncontrollable thermal runaway is to suppress the rate of oxygen release from the positive electrode active material. And to that end, it can be said that controlling the particle size of the primary particles of the composite oxide as disclosed herein is effective.

[0035] [Chemical structure] As long as it is a composite oxide containing at least lithium, a transition element, and oxygen, the chemical structure of the composite oxide is not particularly limited.

[0036] The transition element is not particularly limited as long as it is an element belonging to Groups 3 to 11 of the periodic table, but it is preferable to use at least nickel. By using nickel as the transition metal, the battery capacity can be increased.

[0037] Specific examples of the composite oxides that can be used include the following: lithium cobalt oxide (LiCoO2), lithium nickel oxide (LiNiO2), lithium manganate (LiMnO2), lithium manganese spinel (LiMn2O4), general formula Li a Ni 1-b-c Mn b M<00(00012>O2 (where M is at least one element other than Li, Ni, Mn, and O, 0.95 ≦ a ≦ 1.15, and 0 ≦ b + c ≦ 0.70), a composite oxide having a layered rock salt structure (here, a part of Ni in lithium nickel oxide is substituted with other elements), lithium vanadium compound (LiV2O5), olivine LiMPO4 (where M is at least one element selected from Co, Ni, Mn, Fe, Mg, Nb, Ti, Al, and Zr; or VO), lithium titanate (Li4Ti5O<( 12 )、LiNiaCo b Al c O2 (0.9 < a + b + c < 1.1), etc.

[0038] Among the above composite oxides, lithium-nickel composite oxide is preferable, and more preferably, it has a layered rock salt structure and a general formula Li a Ni 1-b-c Mn b M cA lithium-nickel composite oxide represented by O2 (wherein M is at least one element other than Li, Ni, Mn, and O, and 0.95 ≤ a ≤ 1.15 and 0 ≤ b + c ≤ 0.70) is used. Specific examples of usable elements M other than Li, Ni, and O include: Co, Al, Mn, Ti, Mg, Zn, Nb, W, Mo, Sb, V, Cr, Ca, Fe, Ga, Sr, Y, Ru, In, Sn, Ta, Bi, Zr, B, etc. More specific examples include Co, Al, Mn, Mg, Zn, Nb, W, Mo, Sb, V, Cr, Ca, Fe, Ga, Sr, Y, Ru, In, Sn, Ta, Bi, and B. Using such a lithium-nickel composite oxide as the positive electrode active material in a non-aqueous electrolyte secondary battery can increase battery capacity, but it has the characteristic of easily releasing oxygen from its crystal structure, making it prone to thermal runaway. By using a positive electrode active material for a non-aqueous electrolyte secondary battery according to one embodiment of this disclosure, thermal runaway caused by oxygen release can be suppressed, and the high battery capacity of the lithium-nickel composite oxide can be utilized.

[0039] There are no particular limitations on M, but in certain embodiments, M represents Co or Al, or both Co and Al (i.e., both Co and Al are present in the complex). More specifically, M is Co, or both Co and Al. Even more specifically, M is both Co and Al.

[0040] Furthermore, there are no particular restrictions on b+c as long as it is within the range of 0 ≤ b+c ≤ 0.70, for example, it may be 0.65 or less, 0.60 or less, 0.55 or less, 0.50 or less, 0.45 or less, 0.40 or less, 0.35 or less, 0.30 or less, 0.25 or less, or 0.20 or less. A small b+c means a high nickel content. A high nickel content tends to increase the amount of oxygen released, making thermal runaway more likely. On the other hand, with a positive electrode active material for a non-aqueous electrolyte secondary battery according to one embodiment of this disclosure, thermal runaway can be suppressed even when using a compound with a high nickel content.

[0041] In certain embodiments, 0 < b + c ≤ 0.70, that is, at least one of Mn and M is present in the composite. Preferably, 0 < b + c ≤ 0.60, more preferably 0.05 ≤ b + c ≤ 0.50, particularly 0.05 ≤ b + c ≤ 0.40, more particularly 0.05 ≤ b + c ≤ 0.30, specifically 0.10 ≤ b + c ≤ 0.25 or 0.15 ≤ b + c ≤ 0.20.

[0042] Preferably, 0.98 ≤ a ≤ 1.10, more preferably 1.00 ≤ a ≤ 1.10.

[0043] In certain embodiments, the composite oxide is one of the formula Li a Ni 1-b-c1-c2 Mn b Co c1 Al[[ID=I7]] c2 O₂, where 0.95 ≤ a ≤ 1.15, 0.75 ≤ [1 - b - c1 - c2] ≤ 0.90, 0.01 ≤ b ≤ 0.10, 0.05 ≤ c1 ≤ 0.20, and 0 ≤ c2 ≤ 0.05. In another certain embodiment, the composite oxide is one of the formula LiaNi 1-b-c1-c2 Mn b Co c1 Al c2 O₂, where 0.98 ≤ a ≤ 1.10, 0.80 ≤ [1 - b - c1 - c2] ≤ 0.85, 0.02 ≤ b ≤ 0.08, 0.10 ≤ c1 ≤ 0.15, and 0 ≤ c2 ≤ 0.03. In a specific embodiment, the composite oxide is one of the formula LiaNi 1-b-c1-c2 Mn b Co c1 Al c2 O₂, where 1.04 ≤ a ≤ 1.05, 0.82 ≤ [1 - b - c1 - c2] ≤ 0.84, 0.04 ≤ b ≤ 0.06, 0.11 ≤ c1 ≤ 0.13, and 0 ≤ c2 ≤ 0.02. In another specific embodiment, the composite oxide is one of the formula Li a Ni 1-b-c1-c2 Mn b Co c1 Al c2It is one of the O2 compounds, where 1.04 ≤ a ≤ 1.05, 0.82 ≤ [1-b-c1-c2] ≤ 0.84; 0.04 ≤ b ≤ 0.06; 0.11 ≤ c1 ≤ 0.13, and 0 ≤ c2 < 0.02. In a very specific embodiment, the composite oxide is of the formula Li a Ni 1-b-c1-c2 Mn b Co c1 Al c2 It is one of the O2 values, 1.04 ≤ a ≤ 1.05, 0.82 ≤ [1-b-c1-c2] ≤ 0.84, and 0.04 <b≦0.06であり、0.11<c1≦0.13であり、0<c2<0.02である。

[0044] However, controlled oxygen release and consequently suppression of thermal runaway can also be achieved with composite materials other than those in the specific embodiments described above, provided that the claimed volume-based primary particle size frequency distribution characteristics are met.

[0045] [Primary particles] Primary particles of a composite oxide refer to the smallest unit of particulate matter in which no grain boundaries exist, as observed when a composite oxide powder is viewed with a field emission scanning electron microscope.

[0046] Figure 1A is an example of a scanning electron microscope image of a composite oxide. Figure 1B shows the same scanning electron microscope image of the composite oxide in Figure 1A, with primary particles enclosed by dashed lines. As shown in Figures 1A and 1B, fine particles without grain boundaries are defined as primary particles.

[0047] Primary particles may aggregate to form secondary particles, simply exist as primary particles, or be mixed with secondary and primary particles. As long as the particle size distribution of primary particles is the same, the temperature at which oxygen is released from the composite metal oxide does not change significantly regardless of the state of the primary particles.

[0048] Furthermore, when primary particles aggregate to form secondary particles, a single secondary particle may contain multiple primary particles exhibiting specific peaks, or it may contain multiple types of secondary particles, each formed by the aggregation of primary particles exhibiting the same specific peak.

[0049] (Specific peak) When the volume-based particle size frequency distribution of primary particles is separated into multiple peaks, a particular peak includes a principal peak that represents the maximum peak area and at least one peak having an area ratio of 0.1 to 1 relative to the area of ​​the principal peak.

[0050] The particle size frequency distribution is determined by the following method: Using a field emission scanning electron microscope (e.g., JSM-7100F: manufactured by JEOL Ltd.), electron microscope images are observed at an acceleration voltage of 10kV and a magnification of 3000 to 20000x. Specifically, one field of view in which at least 100 primary particles with visible outlines are observed is randomly selected, and electron microscope images are obtained for all particles with visible outlines from within that field of view, changing the magnification within the above range as needed. For example, if there is a large difference in particle size and the outlines of the particles cannot be observed at 1x magnification in one field of view, the electron microscope images may be divided into multiple images as needed. The equivalent spherical diameter is calculated using image processing software (e.g., ImageJ), and this is used as the particle size of the primary particles. In this case, the scale displayed on the electron microscope image is used as the reference.

[0051] From the obtained primary particle size data, a kernel density distribution (number-based) is calculated using a standard normal distribution as the kernel function. Then, the primary particles are approximated as spheres, and the volume-based particle size frequency distribution is obtained from the number-based distribution. Note that in the volume-based particle size frequency distribution, the logarithm of the particle size is used on the x-axis. Furthermore, the reliability of the bandwidth parameter h related to the distribution is determined by referring to Silverman's bandwidth (see equation (1) below) (Silverman, BW: Density Estimation for Statistics and Data Analysis. Chapman & Hall, London-New York, 1986, 175).

[0052]

number

[0053] The volume-based particle size frequency distribution obtained in this way is fitted using a log-normal distribution function and separated into peaks to calculate the particle size at the peak top of each peak (central particle size of the primary particle) and the peak area of ​​each peak.

[0054] Furthermore, if, during peak separation, it becomes clear that some peaks do not meet the criteria for a specific peak (a peak whose area ratio to the area of ​​the main peak is approximately 0.1), those peaks are judged not to be peaks and are ignored, and the peaks are separated again.

[0055] There are no particular restrictions on the peaks corresponding to a specific peak, as long as they have an area ratio of 0.1 to 1 relative to the area of ​​the main peak. These can include area ratios of 0.11 or higher, 0.12 or higher, 0.13 or higher, 0.14 or higher, 0.15 or higher, 0.16 or higher, 0.17 or higher, 0.18 or higher, 0.19 or higher, 0.2 or higher, 0.22 or higher, 0.25 or higher, 0.27 or higher, 0.3 or higher, 0.32 or higher, 0.35 or higher, 0.37 or higher, 0.4 or higher, 0.45 or higher, and 0.5 or higher. By setting the area ratio to a desired value or higher, the thermal runaway suppression effect can be further enhanced.

[0056] If there are multiple peaks that represent the maximum peak area, the peak with the smallest primary particle size at its peak top is designated as the primary peak, and the other peaks that represent the maximum peak area are included in the specific peaks.

[0057] The particle size of primary particles at the peak top of a specific peak is important for the peak to be scattered and is not particularly limited, but the particle sizes of primary particles are preferably 80 nm or larger, 100 nm or larger, 120 nm or larger, 150 nm or larger, 170 nm or larger, 200 nm or larger, 250 nm or larger, 300 nm or larger, 350 nm or larger, 400 nm or larger, and 450 nm or larger. By setting the particle size of primary particles at the peak top of a specific peak to a desired value or higher, the oxygen release temperature can be increased. On the other hand, the particle size of the primary particles at the peak top of a specific peak is preferably 15 μm or less, 14.5 μm or less, 14 μm or less, 13.5 μm or less, 13 μm or less, 12.5 μm or less, 12 μm or less, 11.5 μm or less, 11 μm or less, 10.5 μm or less, 10 μm or less, 9.5 μm or less, 9 μm or less, 8.5 μm or less, 8 μm or less, 7.5 μm or less, 7 μm or less, 6.5 μm or less, 6 μm or less, 5.5 μm or less, 5 μm or less, or 4.5 μm or less. By setting the particle size at the peak top of a specific peak to a value or less, the energy density can be increased, and particle damage and the deterioration of rate characteristics associated with the cycle can be suppressed.

[0058] The ratio of primary particle sizes (large particle diameter / small particle diameter) at the peak tops of adjacent specific peaks is not particularly limited as long as it is between 1.2 and 8, and is preferably 1.22 or higher, 1.25 or higher, 1.27 or higher, 1.3 or higher, 1.32 or higher, 1.35 or higher, 1.37 or higher, 1.4 or higher, 1.45 or higher, 1.5 or higher, 1.55 or higher, 1.6 or higher, 1.65 or higher, 1.7 or higher, 1.75 or higher, 1.8 or higher, 1.85 or higher, 1.9 or higher, 1.95 or higher, 2 or higher, 2.1 or higher, 2.2 or higher, 2.3 or higher, 2.4 or higher, 2.5 or higher, 2.6 or higher, 2.7 or higher, 2.8 or higher, 2.9 or higher, or 3 or higher. By setting the ratio of primary particle sizes at the peak tops of adjacent specific peaks to a desired value or higher, it is possible to appropriately separate multiple temperatures at which oxygen is released from the composite oxide, and the effect of suppressing thermal runaway can be further enhanced. On the other hand, the ratio of primary particle sizes at the peak tops of adjacent specific peaks is preferably 7.7 or less, 7.5 or less, 7.2 or less, 7 or less, 6.7 or less, 6.5 or less, 6.2 or less, 6 or less, 5.7 or less, 5.5 or less, 5.2 or less, 5 or less, 4.7 or less, 4.5 or less, 4.2 or less, and 4 or less. By setting the ratio of primary particle sizes at the peak tops of adjacent specific peaks to a desired value or less, it is possible to suppress variations in the characteristics of primary particles exhibiting each specific peak.

[0059] Specifically, if a particular peak has four peak tops, and the primary particle diameters of each peak increase in the order A, B, C, and D, then the ratio of the primary particle sizes at the peak tops of adjacent particular peaks is preferably A / B, B / C, and C / D, all within the above range.

[0060] [Maximum oxygen release rate] There is no particular upper limit on the oxygen release rate of the complex oxide, but for example, it is preferably 1.92% or less, 1.9% or less, 1.85% or less, 1.8% or less, 1.75% or less, 1.7% or less, 1.65% or less, 1.6% or less, 1.55% or less, 1.5% or less, 1.45% or less, 1.4% or less, 1.35% or less, 1.3% or less, 1.25% or less, or 1.2% or less.

[0061] The maximum oxygen release rate is determined using a thermogravimetric differential thermal analysis (TG-DTA) instrument (for example, Shimadzu Corporation, DTG-60H) by the following method.

[0062] (Sample preparation) A 2032-type coin cell using lithium as the counter electrode is fabricated according to the method described below. It is charged with a constant current at 0.3C to 4.30V in a 25°C environment, and then charged with a constant voltage until the current reaches 0.05C. After this, it is left to rest for 20 minutes after the charging is complete, then discharged with a constant current at 0.3C to 2.50V, then discharged with a constant current at 0.1C, and then left to rest for 20 minutes. This charge-discharge cycle is repeated twice. After charging with a constant current at 0.3C to 4.30V, it is charged with a constant voltage until the current reaches 0.05C, and then left to rest for 20 minutes after the charging is complete.

[0063] The charged coin cell battery is disassembled in the glove box (dew point below -70°C) without short-circuiting, and the positive electrode is recovered. The recovered positive electrode is washed with DMC for 10 minutes and vacuum-dried in the side box. After this, in the same glove box, the positive electrode compound material is scraped off the Al foil using a spatula. 15 mg of the obtained positive electrode compound material powder is filled into an Al TG measuring container, the lid is closed, and it is sealed with a crimping machine.

[0064] The Al measurement container obtained in this manner is removed from the glove box and placed on the measuring balance of the TG-DTA device.

[0065] (TG-DTA measurement) Reference: Platinum container containing 15-20 mg of Al2O3 Maximum temperature: 600℃ Temperature rise rate: (1) 25℃ (room temperature) ~ 50℃: 1℃ / min (2)50℃~600℃: 5℃ / min Measurement environment: N2 gas atmosphere (200 mL / min).

[0066] Immediately before measurement, a small hole is made in the lid of the aluminum sealed measurement container inside the TG-DTA apparatus under an N2 gas atmosphere, and then the heating is started. This method allows measurement without exposing the cathode compound material powder to the atmosphere.

[0067] Based on the obtained results, a DTG curve was created with temperature on the x-axis and the time derivative of the mass change (TG) on the y-axis (this value is dTG, which represents the mass reduction rate corresponding to the oxygen release rate of the complex oxide). The largest mass reduction rate among the peaks observed in the 150°C to 350°C range was defined as the maximum oxygen release rate (% / min).

[0068] <Method for manufacturing positive electrode active material for non-aqueous electrolyte secondary batteries> The positive electrode active material for a non-aqueous electrolyte secondary battery according to the embodiments of this disclosure can be manufactured, for example, by carrying out the following steps in the order described. In the following description, a method for producing a composite oxide containing 30 mol% or more of Ni among elements other than Li is given as an example, but the method for producing a composite oxide otherwise follows a normal process.

[0069] Step 1: A step of synthesizing a precursor complex compound containing at least a transition metal, and mixing the precursor complex compound with a lithium compound to prepare a mixture; Step 2: A step of firing the mixture prepared in Step 1; Step 3: The composite oxide obtained by calcination in Step 2 is subjected to a water washing treatment as needed; Step 4: A step of applying surface treatment to the composite oxide obtained in Step 2 or 3, if necessary; Step 5: A step in which multiple types of composite oxides with different primary particle sizes and particle size frequency distributions are mixed by changing the conditions of Steps 1 to 3 as needed.

[0070] [Process 1] First, a precursor complex compound is synthesized as an aggregate containing a mass of primary particles, at least one transition metal. There are no particular restrictions on the method of synthesizing the precursor complex compound. For example, an aqueous solution containing an aqueous solution of a transition metal and various aqueous solutions of compounds containing other elements according to the desired composition of the complex oxide is prepared using an alkaline aqueous solution, such as an aqueous sodium hydroxide solution or an aqueous ammonia solution, as the mother liquor. Sodium hydroxide and other substances are added dropwise while monitoring the pH and controlling it to an appropriate range. The precursor complex compound is then obtained by coprecipitation via a wet reaction. For example, the precursor complex compound can be obtained as a hydroxide, an oxide obtained by calcining the hydroxide, or a carbonate.

[0071] Furthermore, after preparing the alkaline aqueous solution that will serve as the mother liquor for the synthesis reaction, it is preferable to create a nitrogen atmosphere inside the reaction tank using an inert gas or industrially preferred nitrogen gas, so that the oxygen concentration inside the reaction tank system and in the solution is as low as possible. If the oxygen concentration is excessively high, the co-precipitated hydroxide may be excessively oxidized by residual oxygen exceeding a predetermined amount, and crystallization may be inhibited, hindering the formation of aggregates.

[0072] The transition metal aqueous solution is not particularly limited, but for example, an acidic aqueous solution is preferably used, and a sulfuric acid aqueous solution such as a nickel sulfate aqueous solution is more preferably used. Furthermore, one or more transition metal aqueous solutions can be used.

[0073] The titanium compound is not particularly limited, but for example, one or more selected from titanium sulfate, titanium dioxide, titanium hydroxide, titanium nitrate, titanium carbonate, titanium chloride, titanium iodide, metallic titanium, etc. can be used.

[0074] The iron compound is not particularly limited, but for example, one or more selected from iron sulfate, iron oxide, iron hydroxide, iron nitrate, iron carbonate, iron chloride, iron iodide, metallic iron, etc., can be used.

[0075] The manganese compound is not particularly limited, but for example, one or more selected from manganese sulfate, manganese oxide, manganese hydroxide, manganese nitrate, manganese carbonate, manganese chloride, manganese iodide, metallic manganese, etc., can be used.

[0076] The cobalt compound is not particularly limited, but it is possible to use one or more selected from, for example, cobalt sulfate, cobalt oxide, cobalt hydroxide, cobalt nitrate, cobalt carbonate, cobalt chloride, cobalt iodide, metallic cobalt, etc.

[0077] The nickel compound is not particularly limited, but for example, one or more can be selected from nickel sulfate, nickel oxide, nickel hydroxide, nickel nitrate, nickel carbonate, nickel chloride, nickel iodide, metallic nickel, etc.

[0078] The niobium compound is not particularly limited, but for example, one or more selected from niobium oxide, niobium chloride, lithium niobate, niobium iodide, etc., can be used.

[0079] The tungsten compound is not particularly limited, but for example, one or more selected from tungsten oxide, sodium tungstate, ammonium paratungstate, tungsten hexacarbonyl, tungsten sulfide, etc., can be used.

[0080] The magnesium compound is not particularly limited, but for example, one or more selected from magnesium sulfate, magnesium oxide, magnesium hydroxide, magnesium nitrate, magnesium carbonate, magnesium chloride, magnesium iodide, metallic magnesium, etc., can be used.

[0081] The aluminum compound is not particularly limited, but for example, one or more selected from aluminum sulfate, aluminum oxide, aluminum hydroxide, aluminum nitrate, aluminum carbonate, aluminum chloride, aluminum iodide, sodium aluminate, metallic aluminum, etc., can be used.

[0082] The zinc compound is not particularly limited, but for example, one or more selected from zinc sulfate, zinc oxide, zinc hydroxide, zinc nitrate, zinc carbonate, zinc chloride, zinc iodide, metallic zinc, etc., can be used.

[0083] For other elements, it is possible to use one or more selected from sulfates, oxides, hydroxides, nitrates, carbonates, chlorides, iodides, metals, etc.

[0084] The proportions of each compound should be appropriately adjusted so that the amounts of each element are in the desired proportions, taking into account the intended composition of the composite oxide.

[0085] There are no particular restrictions on the appropriate pH range when synthesizing the precursor complex compound; it should be determined in a way that yields the desired particle size and coarseness / fineness of the secondary particles, and generally a range of around 10 to 13 is sufficient.

[0086] The precursor complex compound obtained by the wet reaction is preferably subjected to a washing treatment, followed by dehydration and then a drying treatment.

[0087] By subjecting the precursor complex to a washing treatment, impurities that are incorporated into the aggregated particles during the reaction or that adhere to the surface, such as sulfuric acid radicals and carbonate radicals, and the sodium fraction, can be washed away. Suitable washing treatments include Nütsch washing using a Büchner funnel if the amount of impurities is small, and supplying the post-reaction suspension to a press filter for washing and dewatering. While pure water, sodium hydroxide aqueous solution, and sodium carbonate aqueous solution can be used for washing, pure water is preferred from an industrial standpoint. However, if a large amount of sulfuric acid radicals remain, a pH-controlled sodium hydroxide aqueous solution can be used depending on the remaining amount.

[0088] The precursor complex compound synthesized in this manner and the lithium compound are mixed in a predetermined ratio to prepare a mixture. The mixing may be a solvent-based mixture in which the precursor complex compound and the lithium compound are each in the form of an aqueous solution, and these solutions are mixed in a predetermined ratio, or it may be a non-solvent-based mixture in which the powder of the precursor complex compound and the powder of the lithium compound are weighed in a predetermined ratio and mixed by a dry method.

[0089] The lithium compound is not particularly limited, and various lithium salts can be used. Specific examples of lithium compounds that can be used include one or more selected from the following: anhydrous lithium hydroxide, lithium hydroxide hydrate, lithium nitrate, lithium carbonate, lithium acetate, lithium bromide, lithium chloride, lithium citrate, lithium fluoride, lithium iodide, lithium lactate, lithium oxalate, lithium phosphate, lithium pyruvate, lithium sulfate, lithium oxide, etc. Among these, one or more selected from anhydrous lithium hydroxide and lithium hydroxide hydrate are preferably used.

[0090] The mixing ratio of the lithium compound and the precursor complex compound is not particularly limited, but it should be adjusted as appropriate while considering the composition of the complex oxide so that the amount of lithium and the total amount of each element are in the desired proportion.

[0091] [Process 2] In the calcination process for producing composite oxides containing transition metals, lithiation and crystal growth are achieved as described above. However, this process requires a certain oxygen partial pressure for the lithiation reaction. The lithiation reaction yields a lithium-containing composite oxide. After this, crystal growth is promoted by raising the temperature to a predetermined level.

[0092] The maximum temperature of the mixture during firing is preferably 650°C to 1100°C, 670°C to 1000°C, or 700°C to 980°C. Furthermore, the firing time at the maximum temperature is preferably 1 to 24 hours, 1 to 20 hours, 1 to 15 hours, 1 to 10 hours, 2 to 9 hours, or 3 to 8 hours. The desired composite compound can be obtained by setting the maximum temperature and time such that the firing temperature is above the melting point of the lithium compound in the mixture, and the lithium-containing composite oxide achieves the desired crystal growth and particle growth.

[0093] In general, calcination is carried out by weighing lithium compounds, precursor complex compounds, and compound M as needed, mixing them in a mixer to obtain a mixed powder, and then filling this powder into containers such as crucibles or saggars. However, in the lithiumization reaction in particular, it becomes difficult to vent the generated gas to the outside, especially at the bottom of the container filled with the mixed powder, and it becomes difficult to diffuse the required concentration of oxygen. As a result, it becomes difficult to achieve a uniform reaction and to control the particle size of the primary particles.

[0094] Therefore, when manufacturing a composite oxide according to the embodiments of this disclosure, it is preferable to first perform pre-calcination under the following predetermined conditions in step 2, and then perform main calcination under the predetermined conditions. However, pre-calcination is not an essential step.

[0095] In the pre-calcination step 2, a calcination method that particularly promotes the lithiation reaction is preferably employed. Specifically, methods that allow heat to easily act on the mixture, facilitate the release of gases generated by the lithiation reaction, and facilitate the diffusion of gases with a high oxygen partial pressure into the mixture (particles) are desirable. For example, desired properties can be obtained by reducing the amount of mixture subjected to pre-calcination.

[0096] If pre-firing is performed in step 2, the mixture is packed into a sagger or crucible, and firing may be done in a stationary kiln, roller hearth kiln, or pusher kiln, but a rotary kiln may also be used to fire the mixture while it is fluidized.

[0097] The maximum temperature of the mixture to be pre-calcined is not particularly limited and is preferably adjusted according to the type of lithium compound used in preparing the mixture. By this means, a reliable reaction occurs between the precursor complex and the lithium compound in the mixture, the lithiation reaction proceeds uniformly and reliably, no different phases are formed, and the desired complex oxide can be obtained.

[0098] There are no particular restrictions on the atmosphere for pre-calcination; any oxidizing atmosphere that ensures the lithiumization reaction proceeds reliably and uniformly is acceptable. For example, a decarboxylated oxidizing gas atmosphere with a carbon dioxide concentration of 30 ppm or less, or an oxygen atmosphere with an oxygen concentration of 80% to 90% by volume, is preferably used.

[0099] There are no particular restrictions on the duration of the pre-calcination; it should be sufficient for the lithiation reaction to proceed reliably and uniformly. For example, durations of 1 to 10 hours or 2 to 8 hours are preferred.

[0100] Furthermore, to promote crystal and particle growth at higher temperatures, the pre-calcined mixture is subjected to final calcination. In this case, it is necessary to ensure that crystal growth proceeds reliably and uniformly to obtain a composite oxide with the desired crystal structure.

[0101] There are no particular restrictions on the atmosphere used for the final firing; any atmosphere that ensures reliable and uniform crystal growth at an oxygen partial pressure that prevents reduction of transition metals in the mixture being fired is acceptable. Preferably, an atmosphere with low moisture content and carbon dioxide concentration is used. For example, a decarboxylated oxidizing gas atmosphere with a carbon dioxide concentration of 30 ppm or less, or an oxygen atmosphere with an oxygen concentration of 80% to 90% by volume is preferably used.

[0102] The temperature of the main firing is not particularly limited as long as it is higher than the pre-firing temperature, and can be adjusted according to the composition of the composite oxide to be obtained. For example, the maximum temperature is preferably adjusted to 700°C to 1100°C, 710°C to 1000°C, or 720°C to 980°C. By setting the maximum temperature within a desired range, it is possible to obtain a composite oxide with a desired crystal structure and fewer unreacted components, and furthermore, it is possible to prevent a decrease in the battery characteristics of a non-aqueous electrolyte secondary battery using the obtained composite oxide as its positive electrode. Furthermore, for example, when obtaining a composite oxide in which the Ni content among elements other than Li is 20 mol% to 80 mol%, it is preferable to perform the firing within a range in which the maximum temperature of the mixture does not exceed 1100°C.

[0103] There are no particular restrictions on the duration of the final firing; any duration sufficient to form a composite oxide with the desired crystal structure is acceptable. For example, durations of 1 to 15 hours, 2 to 12 hours, or 2 to 10 hours are preferred.

[0104] [Process 3] Furthermore, during the calcination process, unreacted lithium compounds and lithium compounds that have risen to the surface of the particles due to the crystalline structure may be present as impurities in the composite oxide obtained in step 2. For this reason, to remove or reduce these impurities, for example, washing with water or heat treatment may be performed. Note that step 3 is not an essential component.

[0105] [Step 4] Furthermore, the composite oxide obtained in step 2 or 3 may be mixed with a predetermined elemental compound, and a heat treatment may be performed to surface-treat the primary and / or secondary particles of the composite oxide using a compound of lithium and the additive element. This makes it possible to obtain effects such as a reduction in the lithium compound remaining on the particle surface, an improvement in lithium ion conductivity, and a reduction in reaction resistance. Step 4 is not an essential component.

[0106] The elemental compounds added for this surface treatment can be selected from, for example, aluminum compounds, boron compounds, tungsten compounds, manganese compounds, cobalt compounds, phosphorus compounds, niobium compounds, strontium compounds, antimony compounds, zirconium compounds, titanium compounds, etc., and one or more of these can be used.

[0107] [Step 5] If the composite oxide obtained in any of steps 2 to 4 does not have multiple specific peaks on its own, or does not have the specific primary particle size ratio on its own, or if it satisfies specific requirements regarding specific peaks and primary particle size ratio, but you want to further enhance the thermal runaway suppression effect, then multiple types of composite oxides are mixed by changing the manufacturing conditions of the composite oxide (conditions of steps 1 to 4) to change the primary particle size and particle size frequency distribution. Note that step 5 is not an essential component if the composite oxide obtained in any of steps 2 to 4 alone satisfies specific requirements regarding specific peaks and primary particle size ratio.

[0108] Furthermore, the order of steps 3-5 can be changed.

[0109] <Nonaqueous electrolyte secondary battery> The non-aqueous electrolyte secondary battery according to this disclosure comprises a positive electrode containing the above-mentioned composite oxide as a positive electrode active material, and the non-aqueous electrolyte secondary battery comprises a positive electrode, a negative electrode, and an electrolyte solution containing an electrolyte.

[0110] When manufacturing a positive electrode, a conductive agent and a binder are mixed with the composite oxide according to the embodiments of this disclosure using a conventional process. Preferably, the conductive agent is acetylene black, carbon black, graphite, etc. Preferably, the binder is polytetrafluoroethylene, polyvinylidene fluoride, etc.

[0111] The negative electrode is not particularly limited, but for example, in addition to negative electrode active materials such as lithium metal, graphite, and low-crystallinity carbon materials, it is possible to use at least one nonmetal or metallic element selected from Si, Al, Sn, Pb, Zn, Bi, and Cd, or alloys containing these, or chalcogen compounds containing these.

[0112] The solvent for the electrolyte is not particularly limited, but examples include organic solvents containing at least one selected from carbonates such as ethylene carbonate, propylene carbonate, dimethyl carbonate, and diethyl carbonate, and ethers such as dimethoxyethane.

[0113] As an electrolyte, in addition to lithium hexafluoride phosphate (LiPF6) in particular, at least one selected from lithium salts such as lithium perchlorate and lithium tetrafluoroborate can be used dissolved in the solvent. [Examples]

[0114] The present disclosure will be described in further detail below with reference to examples, but the present disclosure is not limited to these examples.

[0115] <Preparation of complex oxides> Composite oxides 1-3 were prepared by the method described below.

[0116] (Preparation of complex oxides 1) Ni 0.83 Co 0.12 Mn 0.05 A nickel-cobalt-manganese composite hydroxide represented by the chemical formula (OH)2 was obtained by coprecipitation. The volume-based D50 of the substantially spherical aggregated particles obtained in this way was 11.2 μm.

[0117] The obtained nickel-cobalt-manganese composite hydroxide, lithium hydroxide, and aluminum hydroxide were weighed and mixed so that Li / (Ni+Co+Mn) = 1.04 and Al / (Ni+Co+Mn) = 0.5 mol%. The mixture was then heat-treated at 570°C for 6 hours under an oxygen atmosphere, and then calcined at 775°C for 6 hours under an oxygen atmosphere (oxygen concentration: 97 vol%). The resulting calcined product was pulverized to obtain lithium nickel composite oxide.

[0118] The obtained lithium nickel composite oxide powder was mixed with 1500 g / L of pure water heated to 25°C to prepare a slurry. The slurry was stirred for 10 minutes, and then dehydrated to obtain a cake-like compound. This cake-like compound was dried in a vacuum dryer at 75°C for 2 hours and then at 120°C for 10 hours.

[0119] To the obtained lithium-nickel composite oxide, 1000 ppm of boron was added as a boron compound, and the mixture was heat-treated at 325°C for 2 hours under an oxygen atmosphere (oxygen concentration: 97 vol%) to obtain composite oxide 1 in which the particle size at the peak top of the primary particle size frequency distribution (central particle size) was 0.5 μm (L1).

[0120] (Preparation of composite oxide 2) Ni 0.83 Co 0.12 Mn 0.05 A nickel-cobalt-manganese composite hydroxide represented by the chemical formula (OH)2 was obtained by coprecipitation. The volume-based D50 of the substantially spherical aggregated particles obtained in this way was 4.1 μm.

[0121] The obtained nickel-cobalt-manganese composite hydroxide and lithium hydroxide powder were weighed and mixed so that Li / (Ni+Co+Mn) = 1.05. The mixture was then calcined at 860°C for 12 hours under an oxygen atmosphere (oxygen concentration: 97 vol%). The resulting calcined material was pulverized, and the supply pressure and grinding pressure were adjusted using a jet mill to prevent the primary particles from being crushed. Afterward, 0.6 mol% aluminum oxide powder (Al2O3) was added, and the mixture was heat-treated at 600°C for 7 hours under an air atmosphere to obtain a lithium metal composite oxide.

[0122] The obtained lithium nickel composite oxide powder was mixed with pure water heated to 25°C at a ratio of 1500 g / L to prepare a slurry. The slurry was stirred for 10 minutes, and then dehydrated to obtain a cake-like compound. The cake-like compound was then dried in a vacuum dryer at 75°C for 2 hours and then at 120°C for 10 hours.

[0123] When 500 ppm of boron was added as a boron compound to the obtained lithium nickel composite oxide, and the mixture was heat-treated at 300°C under air for 7 hours, composite oxide 2 was obtained in which the particle size frequency distribution of primary particles had two peaks when peak-separated, with the particle size (central particle size) of the peak tops of each peak being 1.4 μm (P1) and 2.7 μm (P2).

[0124] (Preparation of composite oxide 3) Ni 0.83 Co 0.12 Mn 0.05 A nickel-cobalt-manganese composite hydroxide represented by the chemical formula (OH)2 was obtained by coprecipitation. The volume-based D50 of the substantially spherical aggregated particles obtained in this way was 4 μm.

[0125] The obtained nickel-cobalt-manganese composite hydroxide and lithium hydroxide powder were weighed and mixed so that Li / (Ni+Co+Mn) = 1.05. Afterward, the mixture was calcined at 850°C for 12 hours under an oxygen atmosphere (oxygen concentration 97 vol%). Then, 0.6 mol% Al2O3 was added as aluminum oxide, and the mixture was heat-treated at 600°C for 7 hours under an air atmosphere to obtain a lithium metal composite oxide.

[0126] The obtained lithium nickel composite oxide powder was mixed with pure water heated to 25°C at a ratio of 1500 g / L to prepare a slurry. The slurry was stirred for 10 minutes, and then dehydrated to obtain a cake-like compound. The cake-like compound was then dried in a vacuum dryer at 75°C for 2 hours and then at 120°C for 10 hours.

[0127] When 500 ppm of boron was added as a boron compound to the obtained lithium nickel composite oxide and heat-treated at 300°C for 7 hours in an air atmosphere, a composite oxide 3 was obtained in which, when the particle size frequency distribution of primary particles was separated by peaks, the particle size at the top of each peak (central particle size) was 1.5 μm (M1), 2.2 μm (M2), and 3.0 μm (M3).

[0128] [Example 1] Composite oxide 1 and composite oxide 2 were mixed so that the peak area ratio was 50:50, and used as a positive electrode active material sample. Figure 2 is a volume-based particle size frequency distribution diagram of the primary particles of the positive electrode active material sample of Example 1. Furthermore, Figure 3 is the DTG curve of the positive electrode active material sample of Example 1.

[0129] [Example 2] Composite oxide 1 and composite oxide 2 were mixed so that the peak area ratio was 81:19 and used as a positive electrode active material sample. Figure 4 is a volume-based particle size frequency distribution diagram of the primary particles of the positive electrode active material sample of Example 2. Furthermore, Figure 5 is the DTG curve of the positive electrode active material sample of Example 2.

[0130] [Example 3] Only composite oxide 2 was used as the positive electrode active material sample. Figure 6 is a volume-based particle size frequency distribution diagram of the primary particles of the positive electrode active material sample of Example 3. Furthermore, Figure 7 is the DTG curve of the positive electrode active material sample of Example 3.

[0131] [Example 4] Only composite oxide 3 was used as the positive electrode active material sample. Figure 8 is a volume-based particle size frequency distribution diagram of the primary particles of the positive electrode active material sample of Example 4. Furthermore, Figure 9 is the DTG curve of the positive electrode active material sample of Example 4.

[0132] [Comparative Example 1] Only composite oxide 1 was used as the positive electrode active material sample. Figure 10 is a volume-based particle size frequency distribution diagram of the primary particles of the positive electrode active material sample of Comparative Example 1. Furthermore, Figure 11 is the DTG curve of the positive electrode active material sample of Comparative Example 1.

[0133] <Rating> The obtained samples were evaluated using the method described below.

[0134] [Compositional analysis of precursor compounds and complex oxides] The composition of the precursor complex and cathode active material particles was measured by the following method. A 0.2 g sample of cathode active material was heated and dissolved in 25 mL of 20% hydrochloric acid aqueous solution. After cooling, the solution was transferred to a 100 mL volumetric flask, and pure water was introduced to prepare the adjusted solution. The elements in the obtained adjusted solution were quantified using ICP-AES (Optima 8300, PerkinElmer).

[0135] [Average aggregate particle size of precursor compound (D 50 )] The particle size distribution was measured using a wet laser method with a laser particle size distribution analyzer (Microtrac HRA, manufactured by Nikkiso Co., Ltd.), based on volume.

[0136] [Scanning electron microscopy observation and creation of particle size frequency distribution] The obtained positive electrode active material samples were observed using a field emission scanning electron microscope (JSM-7100F: manufactured by JEOL Ltd.) at an acceleration voltage of 10kV and a magnification of 3000 to 20000x. Specifically, one field of view in which more than 100 primary particles whose outer shape could be confirmed was randomly selected, and electron microscope images were obtained of all particles whose outer shape could be confirmed from among the particles contained in that field of view, while changing the magnification within the above range as needed. The equivalent diameter of a sphere was calculated from the electron microscope images using image processing software (ImageJ, etc.), and this was used as the particle size of the primary particles.

[0137] From the obtained primary particle size data, a kernel density distribution (number-based) was calculated using a standard normal distribution as the kernel function. Subsequently, the primary particles were approximated as spheres, and a volume-based particle size frequency distribution was obtained from the number-based distribution. In the volume-based particle size frequency distribution, the logarithm of the particle size was used on the x-axis. Furthermore, the reliability of the bandwidth parameter h related to the distribution was determined by referring to Silverman's bandwidth (Silverman, BW: Density Estimation for Statistics and Data Analysis. Chapman & Hall, London-New York, 1986, 175). The volume-based particle size frequency distribution thus obtained was fitted using a log-normal distribution function and separated into peaks. The particle size at the peak top of each peak (central particle size of the primary particles) and the peak area of ​​each peak were calculated.

[0138] Furthermore, if any peaks that did not meet the specific peak criteria (peaks with an area ratio of less than 0.1 to the main peak) were found during peak separation, those peaks were deemed not to be peaks and were ignored, and the peaks were separated again. For example, P1 in Example 2 was ignored because it did not meet the specific peak criteria.

[0139] [Thermogravimetric differential thermal analysis] To confirm the oxygen release behavior of the positive electrode active material sample, thermogravimetric differential thermal analysis (TG-DTA) was performed using a thermogravimetric differential thermal analyzer (DTG-60H, manufactured by Shimadzu Corporation).

[0140] (Sample preparation) A 2032-type coin cell using lithium as the counter electrode was fabricated according to the method described below. It was charged with a constant current at 0.3C to 4.30V in a 25°C environment, followed by constant voltage charging until the current reached 0.05C. After this, the battery was rested for 20 minutes, then discharged with a constant current at 0.3C to 2.50V, followed by constant current discharge at 0.1C, and then rested for 20 minutes. This charge-discharge cycle was repeated twice. Alternatively, the battery was charged with a constant current at 0.3C to 4.30V, then charged with a constant voltage until the current reached 0.05C, and rested for 20 minutes after charging.

[0141] A charged coin cell battery was disassembled in a glove box (dew point below -70°C) to prevent short circuits, and the positive electrode was recovered. The recovered positive electrode was washed with DMC for 10 minutes and vacuum-dried in a side box. After that, the positive electrode compound material was scraped off the aluminum foil using a spatula in the same glove box. 15 mg of the obtained positive electrode compound material powder was filled into an aluminum TG measuring container, the lid was closed, and it was sealed with a crimping machine.

[0142] The Al measurement container obtained in this manner was removed from the glove box and placed on the measuring balance of the TG-DTA apparatus.

[0143] (TG-DTA measurement) Reference: Platinum container containing 15-20 mg of Al2O3 Maximum temperature: 600℃ Temperature rise rate: (1) 25℃ (room temperature) ~ 50℃: 1℃ / min (2)50℃~600℃: 5℃ / min Measurement environment: N2 gas atmosphere (200 mL / min).

[0144] Immediately before measurement, a small hole was made in the lid of the aluminum measuring container inside the TG-DTA apparatus under an N2 gas atmosphere, and the heating process was initiated.

[0145] Based on the results obtained, a DTG curve was created with temperature on the x-axis and the time derivative of the mass change (TG) on the y-axis (this value is dTG, which represents the mass reduction rate corresponding to the oxygen release rate of the complex oxide). The largest mass reduction rate among the peaks observed in the 150°C to 350°C range was defined as the maximum oxygen release rate (% / min).

[0146] [Evaluation of coin cell charging capacity using positive electrode active material samples] In this specification, a 2032 type coin cell using positive electrode active material particles was manufactured using a positive electrode, negative electrode, and electrolyte prepared by the following methods.

[0147] (positive electrode) Acetylene black and graphite were used as conductive agents in a mass ratio of acetylene black:graphite = 1:1, and polyvinylidene fluoride was used as a binder. The positive electrode active material, conductive agent, and binder were blended in a mass ratio of positive electrode active material:conductive agent:binder = 90:6:4, and these were mixed with N-methylpyrrolidone and coated onto aluminum foil. The coated aluminum foil was dried at 110°C to produce sheets, which were punched out to a diameter of 15 mm at 3 t / cm². 2 The positive electrode was formed by rolling.

[0148] (Negative electrode) For the negative electrode, a 500 μm thick lithium foil, punched out to a diameter of 16 mm, was used.

[0149] (electrolyte) A mixed solvent of EC and DMC was prepared in a volume ratio of EC:DMC = 1:2, and a solution was used as the electrolyte by mixing this with 1 mol / L of LiPF6 electrolyte.

[0150] (Separator) A separator punched to a diameter of 20 mm (Celgard #2400 manufactured by Celgard) was used.

[0151] (Measurement of total charging capacity) Using the coin cell prepared by the method described above, constant current charging was performed at 0.3C to 4.30V at 25°C, followed by constant voltage charging until the current reached 0.05C. After this, the system was rested for 20 minutes, then discharged at 0.3C to 2.50V, followed by constant current discharge at 0.1C, and then rested for another 20 minutes. This charge-discharge cycle was repeated twice. After constant current charging at 0.3C to 4.30V, constant voltage charging was performed until the current reached 0.05C. In this operation, the total charging capacity (mAh / g) was calculated using the following method: First charge / discharge cycle: 0.3C at 4.3V (constant voltage charging until 0.05C is reached) 20-minute break Discharge to 2.5V at 0.3C, then discharge again to 2.5V at 0.1C. 20-minute break Second charge / discharge cycle: 0.3C at 4.3V (constant voltage charging until 0.05C is reached) 20-minute break Discharge to 2.5V at 0.3C, then discharge again to 2.5V at 0.1C. Third charge: 0.3C at 4.3V (constant voltage charging until 0.05C is reached) Total charging capacity = 1st charging capacity + (2nd charging capacity - 1st discharge capacity at 0.3C - 1st discharge capacity at 0.1C) + (3rd charging capacity - 2nd discharge capacity at 0.3C - 2nd discharge capacity at 0.1C).

[0152] Table 1 shows the peak area ratio, the area ratio of other specific peaks to the main peak, the central particle size ratio of adjacent specific peaks, the total charge / discharge capacity, the DTG peak top temperature, the maximum oxygen release rate, and the rate of decrease in the maximum oxygen release rate compared to Comparative Example 1 for the composite oxides constituting the samples of Examples 1-4 and Comparative Example 1.

[0153] [Table 1]

[0154] As can be seen from the results in Table 1, when multiple specific peaks are present and the central particle size ratio of all specific peaks is within a predetermined range, it is possible to reduce the maximum oxygen release rate compared to Comparative Example 1, which has only one specific peak.

Claims

1. A method for using a positive electrode active material comprising a composite oxide containing at least lithium, a transition metal, and oxygen, for suppressing or avoiding thermal runaway in a non-aqueous electrolyte secondary battery, When the volume-based particle size frequency distribution of the primary particles of the composite oxide is separated into multiple peaks, these peaks include the following specific peaks: A main peak that shows the maximum peak area, and at least one peak having an area ratio of 0.1 to 1 with respect to the area of ​​the main peak. Includes, A method of use in which the ratio of primary particle size (large particle size / small particle size) at the peak tops of adjacent specific peaks is 1.2 to 8 in all cases.

2. A method for using the positive electrode active material according to claim 1, for controlling the release of oxygen from the positive electrode active material.

3. The method of use according to claim 1 or 2, wherein the composite oxide is a lithium-nickel composite oxide.

4. The lithium-nickel composite oxide has a layered rock salt structure, and its general formula is Li ａ Ni １－ｂ－ｃ Mn ｂ M ｃ O ２ The method of use according to claim 3, represented by the formula (wherein M is at least one element other than Li, Ni, Mn, and O, 0.95 ≤ a ≤ 1.15, and 0 ≤ b + c ≤ 0.70).

5. The method of use according to claim 4, wherein M is selected from one or more of Co, Al, Mn, Ti, Mg, Zn, Nb, W, Mo, Sb, V, Cr, Ca, Fe, Ga, Sr, Y, Ru, In, Sn, Ta, Bi, Zr, and B.

6. The method of use according to claim 5, wherein M is Co or Co and Al.

7. The method of use according to claim 6, wherein M is both Co and Al.

8. Formula Li ａ Ni １－ｂ－ｃ１－ｃ２ Mn ｂ Co ｃ１ Al ｃ２ O ２ (where 0.95 ≦ a ≦ 1.15, 0.75 ≦ [1 - b - c1 - c2] ≦ 0.90, 0.01 ≦ b ≦ 0.10, 0.05 ≦ c1 ≦ 0.20, and 0 ≦ c2 ≦ 0.05), the method of use according to claim 4.

9. The method of use according to claim 1 or 2, wherein the particle size of the primary particles at the peak top of the specific peak is all between 80 nm and 15 μm.

10. A positive electrode active material for a non-aqueous electrolyte secondary battery, wherein the positive electrode active material comprises a composite oxide containing at least lithium, a transition metal, and oxygen. A positive electrode active material for a non-aqueous electrolyte secondary battery, wherein when the volume-based particle size frequency distribution of the primary particles of the composite oxide is separated into multiple peaks, these peaks include a main peak showing the maximum peak area and at least one peak having an area ratio of 0.1 to 1 with respect to the area of ​​the main peak, and the ratio of primary particle sizes (large particle size / small particle size) at the peak tops of adjacent specific peaks is 1.2 to 8 in all cases.

11. The aforementioned composite oxide has a layered rock salt structure, and its general formula is Li ａ Ni １－ｂ－ｃ Mn ｂ M ｃ O ２ The positive electrode active material for a non-aqueous electrolyte secondary battery according to claim 10, which is a lithium-nickel composite oxide represented by the formula (wherein M is at least one element other than Li, Ni, Mn, and O, 0.95 ≤ a ≤ 1.15, and 0 ≤ b + c ≤ 0.70).

12. The positive electrode active material for a non-aqueous electrolyte secondary battery according to claim 11, wherein M is selected from one or more of Co, Al, Mn, Ti, Mg, Zn, Nb, W, Mo, Sb, V, Cr, Ca, Fe, Ga, Sr, Y, Ru, In, Sn, Ta, Bi, Zr, and B.

13. The positive electrode active material for a non-aqueous electrolyte secondary battery according to claim 12, wherein M is Co or Co and Al.

14. The positive electrode active material for a non-aqueous electrolyte secondary battery according to claim 13, wherein M is both Co and Al.

15. Formula Li ａ Ni １－ｂ－ｃ１－ｃ２ Mn ｂ Co ｃ１ Al ｃ２ O ２ A positive electrode active material for a non-aqueous electrolyte secondary battery according to any one of claims 10 to 14, wherein the formula is such that 0.95 ≤ a ≤ 1.15, 0.75 ≤ [1 - b - c1 - c2] ≤ 0.90, 0.01 ≤ b ≤ 0.10, 0.05 ≤ c1 ≤ 0.20, and 0 ≤ c2 ≤ 0.

05.

16. The positive electrode active material for a non-aqueous electrolyte secondary battery according to any one of claims 10 to 14, wherein the particle size of the primary particles at the peak top of the specific peak is all between 80 nm and 15 μm.

17. A non-aqueous electrolyte secondary battery comprising a positive electrode containing the positive electrode active material described in any one of claims 10 to 14.

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